Flywheel magneto ignition apparatus operating with capacitive ignition effect

ABSTRACT

A flywheel magneto ignition system includes a generator coil about which a magnetic field rotates, a first diode connecting a capacitor and the primary winding of an ignition coil to said generator coil, a second diode connected across said generator coil for conducting current pulses blocked by said first diode, a spark plug of the surface type connected in circuit with the secondary winding of the ignition coil, and a control member actuated in respnse to flywheel rotation for controlling current flow to the capacitor and primary winding, the control member being synchronized with the rotating field to initiate charging of the capacitor when a voltage pulse conducted by the second diode has just reached its maximum potential.

United States Patent 1191 Carlsson Sept. 25, 11973 [5 1 FLYWHEEL MAGNETOIGNITION 3,065,382 11/1962 Kleine 317/81 x APPARATUS OPERATING WITH3.500,086 3/1970 Baermann... 310/15 X 3,508,116 4/1970 Burson 317/81CAPACITIVE IGNITION EFFECT 3,584,929 6/1971 Schuette t t r 315/244 [75]Inventor: Hans Thorsten Henrik Carlsson, 3.5 6.133 /19 1 Warr n t a315/209 SC Amal, Sweden [73] Assignee: Aktiebolaget Svenska PrimaryExamlinerfvolodymyr y y El kt t A l S d Attorney-Ben amin H. Sherman eta1. [22] Filed: July 5, 1972 21 Appl. No.: 269,131 1571 ABSTRACT Aflywheel magneto ignition system includes a genera- [30 F i Applicationp i Data tor coil about which a magnetic field rotates, a first July 5swedfin 8698/71 diode connecting a capacitor and the primary winding ofan ignition coil to said generator coil, a second diode [52] U S Cl317/81 123/149 310/15 connected across said generator coil forconducting .3.l 315/24 317 317/96 current pulses blocked by said firstdiode, a spark plug I 320/1 336/1 of the surface type connected incircuit with the sec- [51] Int CI g llzsg 3/00 ondary winding of theignition coil, and a control mem- [58] Field 96 her actuated in respnseto flywheel rotation for controll23/l46 5 3 15/506 ling current flow tothe capacitor and primary winding,

' 320/l.336/1 d the control member being synchronized with the rotatingfield to initiate charging of the capacitor when a [56] References Citedvoltage pulse conducted by the second diode has just reached its maximumpotential. UNITED STATES PATENTS 2,536.468 1/1951 Russell 317/92 5Claims, 5 Drawing Figures PATENTED SEP 2 5 I973 sum 10F 2 Fig. 3

PATENTED SEP25 I975 I SHEET 2 BF 2 Fig. 4

lllllllll'l FLYWHEEL MAGNETO IGNITION APPARATUS OPERATING WITHCAPACITIVE IGNITION EFFECT From the very beginning of the internalcombustion engine era the common way of producing an ignition sparkbetween the electrodes of the spark plug is characterized in that alow-voltage primary current is stepped up in an ignition coil to anoperating voltage of 8 to 9 kilovolts. The source of the primary currentmay be a battery, a DC generator or a magneto. Magnetos are commonlyused in e.g. motor cycle and motor bike motors, outboard motors,small-size stationary or tractor motors for various types of auxiliaryimplements and the like.

In order to establish the spark-over at exactly the right moment, i.e.when the piston is in a predetermined position short of the end of thecompression stroke, systems of this type are provided with a breakerdevice adapted to rotate on the motor shaft or synchronously inconnection therewith, said breaker device being adapted to break theprimary current to the ignition coil thereby causing a quick magneticflux change to take place in the iron core thereof so that an ignitionvoltage is induced in the secondary winding For this reason ignitionsystems of this type have been considered as being inductive ignitionsystems irrespective of the fact that a condenser always is connectedacross the contacts of the breaker in order to attenuate the sparkformation which otherwise always will take place due to the voltagepeaks inductively produced at the mo-' ment the contacts close and open.The charge received by the condenser during breaking is again fed to theprimary circuit and contributes to the energy conversion in the ignitioncoil, i.e. to increase the ignition spark.

During recent years the continuously increasing demands regarding stableoperation over a large range of number of revolutions comprising a lowidling speed, for example 200 revolutions per minute, and high speedsduring operation, such as 8000 to 10,000 revolutions per minute, goodcombustion properties throughout the range of operative speeds and last,but not least, improved starting properties, have initiated an intensivedevelopmen work in the field of so-called condenser igntion systems,i.e. ignition systems based on capacitive spark generation. Thisdevelopment work has been performed in parallel to and in closeconnection with simultaneously performed investigations regarding theignition and combustion process proper taking place in the motor as wellas with attempts to develop novel and improved types of spark plugs. Ithas been the purpose of these investigations to arrive at a combinationof ignition system and spark plug which yields optimal ignition effectthroughout the range of operational speeds, which is practicallyunaffected by fouling in the spark plug, for example due to carbonbridges, soot, oil, excessively rich fuel mixture and the like, andwhich in addition yields efficient ignition and combustion also duringvery low starting speeds, such as 200 revolutions per minute.

For technical and physical reasons these requirements cannot be fullysatisfied by the inductive ignition systems, whereas condensor systemshave proved to offer practically useful solutions yielding particularlygood results. Thus, there arenow on the market both battery andgenerator or flywheel operated condenser systems in combination withso-called surface spark plugs. This latter type of spark plug which hasrecently been developed and which is particularly suited for use inconnection with condenser ignition igniting systems, is distinguishedfrom spark plugs for inductive systems by the fact that it lacksdistinct electrode tips between which spark-over takes place and insteadis provided with a central electrode disposed in a state of insulationin the tubular spark plug body so that the spark plug body and thecentral electrode terminate in approximately the same plane. The sparkwill flash over at any arbitrary point on the annular surface betweenthe central electrode and the tubular body. As a rule, such surfacespark plugs are additionally provided with a preliminary spark gapprovided within the plug and adapted to bring about a change ofdistribution between current and voltage to produce a higher overallvoltage during spark-over. This distribution effect appears to be ofessential importance in condenser systems.

Capacitive ignition systems are essentially based on the fact thatduring each ignition a preliminarily charged condenser is dischargedover the primary winding to an ignition coil due to the fact that acontrol member closes the circuit. The control member may comprise amechanical means corresponding to the breaker switch previouslymentioned in connection with inductive ignition systems or it maycomprise an electronic circuit including, for example, a thyristor, adiode and a trigger coil which for a flywheel magneto ignition apparatusis disposed in the magnetic field of the flywheel so that aposition-determined pulse induced in the trigger coil is rectified bythe diode and renders the thyristor conductive for the primary current.The electronic circuit and all the component parts thereof may becompletely cast into a block of thermosetting resin, such as epoxyresin, and is thus adapted to be attached as a compact and extremelyreliable unit within or outside of the flywheel.

For capacitive ignition systems in combination with surface spark plugscertain basic functional conditions have been established insuringreliable ignition under all operational and starting conditions. Thus,during operation the voltage level must be at 18 20 kilovolts ratherthan the above mentioned range of 8 9 kilovolts in conventionalinductive systems and with normal spark plugs. Moreover, the rising timedefined as a time required for arriving at the voltage necessary forspark-over in a surface spark plug must not exceed 10 microseconds andpreferably be considerably lower, for example, 2 microseconds. Finally,the burning time of the spark must be at least to microsecond. All theseconditions which are based on comprehensive practical tests and whichnow can be considered to be finally established, involve in turnspecific requirements regarding dimensions, construction and choice ofcomponents and the like for the ignition system. For example, it isnecessary to provide for the operating voltage of 18 20 kilovolts asufficient voltage range so that a maximum voltage exceeding 30kilovolts may be obtained. Moreover, consideration must be given to theproperties of the condenser as far as discharge time is concerned and tothe resistance, i.e. inductance in the primary winding of the ignitingcoil which is decisive for the discharge speed of the condenser and thusdirectly influences the rising time. In addition, sufficient energydetermined by the prodact: charging voltage x condenser capacity must beproduced to enable a sufficient burning time (80 to 100 microseconds) ofthe spark to be obtained. In addition, it is a basic requirement for theentire combination that the components should be cheap, reliable andcompact.

In order to satisfy the energy requirement the charging voltage of thecondenser must be on a sufficiently high level. A value of, for example,1000 volts would be desirable. While such a voltage level is actuallyobtainable, it entails on the other hand an unpermissible increase ofthe electronic components (such as the thyristor and diode) and, forthis reason, the charging voltage of the condenser in practice must belimited to a maximum of 500 volts.

In order to produce the charging voltage in flywheel magnetos there isprovided, in a previously known way, a generator coil in the rotatingfield of the flywheel. The alternating voltage generated in thegenerator coil is rectified in a first diode and the current is fed intothe condenser, the control member in the primary circuit being openduring this phase of operation. The supplied current has the characterof a positive half wave pulse having a voltage proportional to thenumber of revolutions of the flywheel. In order to relieve the firstdiode from excessive barrier voltages from the negative half wave of thegenerator coil a second diode may be provided which is connected inparallel overthe generator coil and which produces a current migrationof the negative half wave through the generator coil, this energy beingconsumed by the inductance and essentially transformed into heat. Inthis way the voltage amplitude of the negative half wave may beminimized and the voltage charge of the first diode reduced.

In prior systems of this type it has been attempted to rectify only oneof these half waves or both of them during charge of the condenser. Inother words, the control member has opened in or slightly after thepoint of cross-over between the negative and the positive half wave toinitiate the charge of the condenser. As mentioned previously theapplied voltage will be directly proportional to the number ofrevolutions of the flywheel but will reach maxim'umvalue at-a certainnumber of revolutions whereafter a voltage reduction will take place dueto the increased number of cycles. In order to achieve a sufficientigniting effect during low speeds, i.e. during idling and particularlyduring starting, it is obviously a matter of paramount interest to bringabout as high a charging voltage as possible also during low speeds.However, a limit is established by the mere physical voltage developmentof the positive half wave which cannot be exceeded and which preventsstarting speeds Iower than about 500 revolutions per minute from beingachieved.

Through the present invention, which is based on the fact that also thenegative half wave yet without rectification is used for charging thecondenser, this limitation is eliminated so that a reliable start may beobtained also at, for example, 200 revolutions per minute even if thespark plug should be heavily soiled.

The characterizing features of the invention will appear from theattached claims.

An embodiment of the invention is described hereafter by reference tothe enclosed drawings.

current in the form of a mechanical breaking and closing switch. 1

FIG. 2 shows the same circuit diagram as FIG. 1, however, having thecontrol member constructed as an electronic circuit comprising athyristor and a trigger coil with a diode connected in series.

FIG. 3 shows a diagram indicating the relationship between voltage andnumber of revolutions from a generator coil of the system as illustratedin respectively FIGS. 1 and 2.

FIG. 4 shows a diagram of the charging voltage from a generator coilbelonging to the system according to respectively FIGS. 1 and 2 to acondenser, a negative, diode-controlled half wave and a positive halfwave being illustrated.

FIG. 5 is a diagram showing in relation to time the ignition voltageemanating from an ignition coil provided in the system according torespectively FIGS. 1 and 2.

In FIGS. 1 and 2 a generator coil 1 having an iron core 2 is connectedby a first terminal to ground at 3 and by another terminal to a branchpoint 4. From branch point 4 a line extends to a first diode 5 andanother line to a second diode 6. This latter diode is connected toground at 7. The first diode 5 is connected to another branch point 8.Both diodes 5 and 6 are adapted to conduct current in a directionindicated by the arrow in the diode symbols and to block flow of currentin the opposite direction. In FIG. 1 a line extending from branch point8 leads to a mechanical control member generally designated as 9 andcomprising a contact arm 10 adapted respectively to open and close aline 11 connected to ground at 12. Contact arm 10 is operated by a cammember 29 provided on the motor shaft and firmly connected thereto androtating therewith, the construction of the contact arm 10 and cammember being such that for every ignition the cam by means of contactarm 10 brings about a breaking and closing action between branch point 8and ground connection 12. The closing action in this case takes place inthe exact instant when the ignition in the cylinder is to be performed.According to the invention the breaking action is to take place at aninstant defined below.

In FIG. 2there is shown an alternative embodiment of the conrol membercomprising a thyristor 13 which is connectedto ground at a point 14;Opening and closing of thyristor 13 is determined by a current pulsefrom a trigger coil 15 provided with an iron core 15' and by means of aterminal connected to ground at 16 and by another terminal connected toa branch point 17 via a diode 17'. In accordance with conventionalpractice a predetermined resistance 18 is connected between point 17 andthe line connecting thyristor l3 and ground connection 14, resistor 18determining the voltage from trigger coil 15 at which the thyristor 13will respectively break and close the current in the direction frombrach point 8 to ground connection 14.

It is also possible to determine opening and closing of the thyristor bymeans of two or more trigger coils 15, whereby it is possible to obtaina greater variation of the control action.

In both FIGS. 1 and 2 a condenser 19 is connected on the one hand tobranch point 8 and on the other hand to a branch point 20. An ignitioncoil generally designated as 23 and having an iron core 24 is attachedby means of one terminal from a primary winding 21 and one terminal froma secondary winding 22 to branch point 20. Another terminal from primarywinding 21 is connected to ground at 25 and another terminal fromsecondary winding 22 is connected to an electrode 26 insulated inrelation to ground and belonging to a surface spark plug generallydesignated as 27 the other electrode 28 of which is connected to ground.

It appears from FIGS. 1 and 2 that the exemplary systems shown areidentical except as far as the control members are concerned. In bothcases the generator coil 1 is so disposed in the rotating fieldemanating from a flywheel conventionally comprising permanent magnets,that an alternating current is produced in the generator coil 1. In thealternative embodiment according to FIG. 2 trigger coil 5 must besuitably disposed in the rotating field of the flywheel in such a waythat the required voltage change acting respectively to open and toclose the thyristor is obtained in the exactly correct instance of timerequired by the invention.

The voltage generated in the generator coil 1 is dependent on the numberof revolutions of the flywheel in a way fundamentally shown in FIG. 3 inwhich a curve A indicates the voltage along an axis V independence ofthe number of revolutions along an axis n. Within a first range ofnumbers of revolutions -n, the voltage quickly goes up to a maximumvalue V, of for example 500 volts and thereafter decreases slightly dueto the increase of the inductance in the coil circuit caused-by theincreased cycle number.

The voltage wave which is generated upon every complete magnetic fieldpassage in the generator coil is illustrated in FIG. 4 by a curvegenerally designated as B, the time T being indicated on an x-axis andthe voltage being plotted on a y-axis. A negative half wave isdesignated as B, and a positive half wave as B, the provision being madeas far as the negative half wave B, is concerned that the second diode 6is completely disconnected from the circuit of the generator coil ll. Insuch a case the two half waves B, and B, will be fully congruent butinverted. By the current-directing effect from the other diode 6,provided this diode is connected as shown in respectively FIGS. 1 and 2,the circuit comprising the second diode 6 and the generator coil l isclosed, the negative half wave B, producing a current via the diodethrough the generator coil ll causing the voltage to be reduced asfundamentally indicated by curve B in FIG. 4. This current and thevoltage reduction produced are dependent on the windings of the coil,the dimensions of the wire, the iron core etc. and may be varied withincertain limits. It is also possible to achieve by outer resistors orsimilar devices such an adaptation that the most appropriate course ofcurve B in respect to the invention is obtained.

It appears from respectively FIGS. 1 and 2 that the charging ofcondenser 19, irrespective of the course of the voltage according tocurves B, and B, respectively, will start only in the instant whencontrol member 9 and 13 respectively will be opened, for when thecontrol member is closed a current passes through the first diode 5directly to ground connection 12. Another condition which must befulfilled in order that charging shall take place is of course that thechange of voltage for curves B and B, respectively has the rightdirection for diode 5, i.e. increases with time (and thus has a positiveslope according to FIG. 4).

According to the invention the control member 9 and 13 respectively openat or immediately after the instant when curve B has arrived at itsnegative maximum, i.e.

point P, in FIG. 41. The charging voltage to condenser 19 will thenobtain a voltage contribution V, which is added to the maximum voltageV, of the positive half wave. Moreover, the interval of time between theopening point P, and the ensueing closing of the control member is sochosen that condenser 19 is enabled to receive the total voltage sum V VWhen the control member 9 and 13 respectively again closes discharge ofthe condenser 19 takes place via control member 9 and ll3 respectively,ground connection 12 and 14 respectively and ground connection 25through the primary winding 21 to ignition coil 23 via branch point 20.This discharge generates a voltage pulse in the secondary windng 22 andproduces a spark in surface spark plug 27 having the properties asdescribed previously.

The voltage development during discharge is illustrated in FIG. 5 as afunction of time, the voltage V being plotted along an y-axis and time Talong a x-axis. A solid line curve 13;, represents a normal voltagedevelopment during a spark-over in the spark plug, a maximum valueV,,possibly being found at 18 to 20 kilovolts. A broken curve Bindicates the voltage marginally present with a voltage top V of forexample 30 kilovolts.

Dueto the fact that according to the invention the charging of thecondenser 19 is started within the range of the negtive half wave B FIG.4, the above mentioned, particularly desirable technical featureseffects effects, as far as reliable ignition at low idling speeds andlow starting speeds are realized. This is shown in FIG. 3 by a curve A,representing the charge voltage of condenser 19 in the arrangementaccording to the invention, whereas curve A, indicates the chargingvoltage in conventional systems. Voltage curve A increases more quicklythan voltage curve A, to such an extent that the required chargingvoltage V, is obtained at a starting speed n, in curve A, which may beless than half the starting speed n for curve A,.

In addition the important fact is to be observed that the voltagedevelopment of the negative half wave, curve 8,, FIG. 4, onlyinsignificantly is dependent on the number of revolutions which meansthat the voltage sum V V never can reach values dangerous for diode 5.

The practical adaptation of the invention to the mechanical controlmember 9 is simple to perform and in volves shaping the cam controllingcontact arm in such a way that contact arm 10 will respectively open andclose the circuit as described.

In an analogous way, in the electronic control member according to FIG.2, the trigger coil 15 is arranged so that the diode will respectivelyopen and close at the described moments.

Practical tests performed with a device according to the invention havegiven excellent results. By deliberate total soiling, such as byapplication of thick gear box oil or similar material, the spark plughas been brought into such a condition that starting with the aid ofordinary condenser ignition systems has been possible only at 500 to 600revolutions per minute. With the aid of the device according to theinvention, a complety reliable start has been achieved at speeds as lowas 200 revolutions per minute. Moreover, fully reliable idling has beenachieved at low speeds. Thus, the invention involves an importantprogress on the field of capaci-' tive ignition as applied to flywheelmagneto igniting apparatus.

What is claimed is: 1. A flywheel magneto ignition system for aninternal combustion engine, comprising:

a. means on the flywheel having a magnetic field with at least one polerotatable about the flywheel axis; b. a generator coil disposed in therotatable magnetic field and inductively responsive thereto to provideat least one negative half-wave and positive halfwave as each said polepasses thereby; c. a first diode connected to said generator coil; d. asecond diode connected across said generator coil and oriented toconduct current pulses blocked by said first diode;

rent from said coil as rectified by said first diode;

f. an ignition coil having a primary winding in circuit with the otherside of said capacitor, and having a secondary winding;

g. a spark plug of the surface type connected in circuit with saidsecondary winding; and

h. a control member actuated in response to flywheel rotation forcontrolling current flow to said capacia capacitor connected at one sideto receive cur-.

tor and said primary winding, said control member being synchronizedwith the rotating field to initiate charging of the capacitor when avoltage pulse conducted by said second diode has just reached itsmaximum potential.

2. A system according to claim 1 in which said control member is aswitch controlled by a cam on the flywheel shaft and synchronouslyrotating therewith.

3. A system according to claim 2 in which the cam is shaped to open saidswitch to initiate said charging and to close said switch when saidcapacitor is fully charged and ignition is to take place.

4. A system according to claim 1 in which said control member comprises:

a. a thyristor,

b. a third diode, and

c. at least one trigger coil disposed in said rotatable field andconnected in series with each other.

5. A system according to claim 4 in which said trigger coil is sodisposed in the rotatable field as to open said thyristor to initiatesaid charging and to close said thyristor when said capacitor is fullycharged and ignition is to take place.

1. A flywheel magneto ignition system for an internal combustion engine,comprising: a. means on the flywheel having a magnetic field with atleast one pole rotatable about the flywheel axis; b. a generator coildisposed in the rotatable magnetic field and inductively responsivethereto to provide at least one negative half-wave and positivehalf-wave as each said pole passes thereby; c. a first diode connectedto said generator coil; d. a second diode connected across saidgenerator coil and oriented to conduct current pulses blocked by saidfirst diode; e. a capacitor connected at one side to receive currentfrom said coil as rectified by said first diode; f. an ignition coilhaving a primary winding in circuit with the other side of saidcapacitor, and having a secondary winding; g. a spark plug of thesurface type connected in circuit with said secondary winding; and h. acontrol member actuated in response to flywheel rotation for controllingcurrent flow to said capacitor and said primary winding, said controlmember being synchronized with the rotating fiEld to initiate chargingof the capacitor when a voltage pulse conducted by said second diode hasjust reached its maximum potential.
 2. A system according to claim 1 inwhich said control member is a switch controlled by a cam on theflywheel shaft and synchronously rotating therewith.
 3. A systemaccording to claim 2 in which the cam is shaped to open said switch toinitiate said charging and to close said switch when said capacitor isfully charged and ignition is to take place.
 4. A system according toclaim 1 in which said control member comprises: a. a thyristor, b. athird diode, and c. at least one trigger coil disposed in said rotatablefield and connected in series with each other.
 5. A system according toclaim 4 in which said trigger coil is so disposed in the rotatable fieldas to open said thyristor to initiate said charging and to close saidthyristor when said capacitor is fully charged and ignition is to takeplace.